1. Field of Disclosure
The present disclosure relates to cooling barges, in particular, enhancing closed loop cooling systems by improving the effectiveness of heat removal through hull mounted coolers on refrigerated barges.
2. Description of the Related Art
Barges are used to transport cargo on the ocean and inland waterways. When refrigeration of the cargo is desirable or required, controlling the temperature inside the barge requires specialized equipment, additional costs, and energy to maintain the appropriate low temperatures during transport or when the barge is docked. Cargoes such as liquid natural gas (LNG), ammonia or anhydrous ammonia, and liquid propane gas (LPG) are stored as liquids at lower temperatures and, in some instances, high pressures. Anhydrous ammonia stored as a liquid near normal atmospheric pressures must be cooled below −28 degrees F. (−33 degrees C.). Typically, boats and barges include coolers mounted on or near the outer hull (heat exchangers) below the water line and use the surrounding water at an ambient water temperature as a heat sink. Thus, the heat exchangers remove internal heat of the barge to the ambient temperature water environment. The internal heat may be due to the cargo, the refrigeration system used to maintain the cargo at low temperatures, and additional equipment operating in the refrigerated barge.
Removing the heat (cooling) may be performed by a closed-loop cooling system that pumps a fluid that circulates through pipes and into internal systems and bulkheads to draw heat out of the interior of the barge to the outer hull, where a heat exchanger may be disposed. Thus, the heat moves from the interior of the barge to the heat exchanger by way of the closed-loop cooling system. One or more suitable heat exchangers, such as box coolers, cooling fins, or grid coolers, may be disposed on or in the outer hull. Contact with the surrounding water provides cooling of the heat exchanger so that heat flows out of the barge and into the ambient environment. The heat exchanger is cooled by conduction (when the barge is motionless or only slightly moving relative to the water) or by convection and conduction (when the barge is moving relative to the water) due to the surrounding water (i.e. sea or river water) in contact with the outer surface of the cooler. The heat exchanger removes heat at its lowest rate when the barge is motionless, since there is no heat removal by convection. Since coolers are usually mounted directly to the outside of the hull, only the outer side of the cooler is in contact with the flow of water.
One of the shortcomings closed-loop cooling systems with outer hull mounted heat exchangers on barges is that the effectiveness of the heat transfer from the barge to the water is heavily depends on movement of the barge through the water. While heat will transfer across any temperature differential, the rate of heat transfer is relatively low when the barge is not moving relative to the water, since only cooling by conducting heat through the water takes place.
A shortcoming of barges with closed-loop cooling systems is that cargo loading is limited by the rate that the cargo can be effectively cooled to a specified temperature. When the barge is docked for loading, the cooling system is least effective, and, the heat load added by the loading of cargo can require the suspension of loading activities until the barge is adequately cooled.
Another shortcoming of barges with closed-loop cooling systems is that the heat transfer maximum is completely dependent on the temperature differential between the closed-loop cooling system and the ambient water temperature for a given relative speed.
Another shortcoming of barges with closed-loop cooling systems and hull mounted coolers is that the ambient temperature water generally only flows across the outer side surface of the cooler, such that heat is not being effectively removed from the inner side of the cooler.
Refrigeration equipment and fuel to operate said refrigeration equipment represent a substantial cost in the operation of a refrigerated barge. Also loading delays due to cargo refrigeration demands exceeding the cooling capacity of the barge's refrigeration system coupled with its cooling system, present scheduling problems and additional costs.
What is needed is an open-loop cooling system to enhance the performance of the existing closed-loop cooling system and heat exchanger. What is also needed is cooling of the inner side of the heat exchanger to improve heat removal to the ambient temperature water. What is also needed is an open-loop cooling system that operates by convection when the barge is immobile relative to the water.